Charge domain mathematical engine and method

ABSTRACT

A multiplier has a pair of charge reservoirs. The pair of charge reservoirs are connected in series. A first charge movement device induces charge movement to or from the pair of charge reservoirs at a same rate. A second charge movement device induces charge movement to or from one of the pair of reservoirs, the rate of charge movement programmed to one of add or remove charges at a rate proportional to the first charge movement device. The first charge movement device loads a first charge into a first of the pair of charge reservoirs during a first cycle. The first charge movement device and the second charge movement device remove charges at a proportional rate from the pair of charge reservoirs during a second cycle until the first of the pair of charge reservoirs is depleted of the first charge. The second charge reservoir thereafter holding the multiplied result.

RELATED APPLICATIONS

This patent application is related to U.S. Provisional Application No.62/637,496 filed Mar. 2, 2018, entitled “CHARGE DOMAIN MATHEMATICALENGINE” in the name of David Schie, and which is incorporated herein byreference in its entirety. The present patent application claims thebenefit under 35 U.S.C § 119(e).

TECHNICAL FIELD

The present invention generally relates to image sensing device and,more particularly to, a charge domain mathematical engine wherein acharge store in a reservoir may be directly coupled to a multiplier of amachine learning input layer.

BACKGROUND

In silicon imaging it is common to rely on the integration or movementof charge using charge domain structures such as spill and fillcircuits, CCD registers, photodetectors, correlated double samplingcircuits, and similar devices. Spill and fill circuits may rely upon theconcept of a buried pinned photodiode, FIG. 1 shows a cross-section viewof a buried pin diode structure 10 showing active doping profiles. Theburied pinned photodiode 10 may integrate electrons created when lightis collected by the buried pinned photodiode 10 into a storage well SWregion. A second charge reservoir, the floating diffusion FD, is createdon the far side of a transfer gate labelled TG.

Referring to FIG. 2A, a spill and fill circuit 20 may be seen. The spilland fill circuit 20 uses the concept of a pinned photodiode (PPD) chargereceptacle holding electrons in front of a transfer gate TG. Thetransfer gate TG is lowered and raised in conformance with requiredelectron flow. At some point the transfer gate TG lowers the potentialbarrier and the electrons spill from the storage well SW chargereservoir into the floating diffusion FD charge reservoir. The devicesare created so as to ensure that all electrons move from the storagewell SW charge reservoir into the floating diffusion FD chargereservoir. FIG. 2B shows the energy diagram from the storage well SWcharge reservoir into the floating diffusion FD charge reservoir.

Referring to FIG. 3, a spill and fill circuit 30 may be seen. The filland spill circuit 30 uses the uses the spill and fill circuit 20 of FIG.2A but includes the concept of a reset device 32 coupled to the transfergate TG and a source follower SF which converts the charge on thefloating diffusion FD charge reservoir to a voltage which may then beread by other circuitry. Typically, correlated double sampling (CDS) maybe used to sample the noise and offset on the output of the floatingdiffusion PD charge reservoir after reset, and then read again after thespill (charge transfer) such that only the difference attributed to thelatest integrated charge stored on the storage well SW remains. By doingthis any offset charge and certain noise is removed.

Instead of two charge reservoirs a single charge reservoir might, beused to produce a weighted input and sum result or a weighted summer.Initially said reservoir would be reset to a known charge level.Thereafter during a first cycle a plurality of input current movementmeans would couple charge from the charge reservoir with each of saidcurrent movement means removing charge at a rate individuallyproportional (in conformance with desired weight values) to an outputcurrent movement means to be used in a second cycle but off during saidfirst cycle. Additionally, each of said plurality of input currentmovement means would be further gated in time, or allowed to move chargeonly during a time, conforming to individual input magnitudes. Theresulting input charge movement magnitude for a gated period of timewould remove a charge conforming to the weighted input magnitude fromsaid charge reservoir. At the end of first cycle, once all inputmovement means have removed their charges, a second cycle would causethe output charge movement means to return the charge in the chargereservoir to its original level. The time it would take to do so wouldbe proportional to the weighted sum of the inputs. The resultingweighted summer thereby accepting inputs as time, weights are chargemovement rate magnitude, and producing an output as a time.

Once the charge is transferred to the floating diffusion FD chargereservoir there are a number of other circuits which may be used inplace of the source follower SF to convert the charge into a voltage orcurrent and thereafter into a digital value. For example, a row of animager may rely on a counter which is compared to each pixel followervalue and the digital words associated with each specific pixelrecorded. There are many circuits which attempt to optimize the speedand power efficiency of the conversion from the charge domain to adigital word.

Machine vision is a common application of artificial intelligence (AI)or machine learning. Autonomous or machine vision augmented vehicles,handset security such as fingerprints or facial recognition, smart citysensors, security cameras, x-ray, ultrasound and medical diagnosis,robotics, drones, wearable heart rate monitors, behavioral analysis andmonitoring and many other applications are relying upon the analysis ofimages for a variety of tasks, many of them time and power critical.

Presently, machine learning systems require that the input be a digitalword or at the very least a voltage, current or spiking waveform (whichis also a voltage or current waveform). The conversion of charge reliesupon a coupling circuit such as the source follower SF shown in FIG. 3all of which are known to be associated with three undesirable sideeffects. The first is a loss of image quality due to introduction ofnoise by the coupling circuit. It is well known by those skilled in theart that any circuit which converts charges maintained in reservoirssuch as the storage well SW or floating diffusion FD regions describedin FIGS. 1-3 to a voltage or current will necessarily introduce noise.This noise for example could degrade an image with 14 bit pixel accuracyto 12 bit equivalent accuracy. In medical or time critical life safetyapplications this could obscure key information. A second side effect ofconversion to the current or voltage domain is the time associated withthe conversion. The digitization of the voltage or current on the outputof the coupling circuit takes time. In an augmented vehicle, life safetyapplication or high-speed imaging application this latency couldliterally mean the difference between a desirable result or a veryundesirable result such as a death or fatality. Finally, the conversionof the information from the charge domain to the voltage or currentdomain and finally digital domain further requires additional energy.This energy is associated with the coupling circuit itself, as well, asthe circuitry related to digitization or creating the desired waveformssuch as a neuromorphic spiking waveform.

Therefore, it would be desirable to provide a system and method thatovercome the above problems. The system and, method would couple thecharge stored in reservoirs directly to multipliers of a machinelearning input layer or weighted summer.

SUMMARY

In accordance with one embodiment, a multiplier is disclosed. Themultiplier has a pair of charge reservoirs. The pair of chargereservoirs are connected in series. A first charge movement deviceinduces charge movement to or from the pair of charge reservoirs at asame rate. A second charge movement device induces charge movement to orfrom one of the pair of reservoirs, the rate of charge movementprogrammed to one of add or remove charges at a rate proportional to thefirst charge movement device. The first charge movement device, or othermechanism, loads a first charge into a first of the pair of chargereservoirs during a first cycle. The first charge movement device andthe second charge movement device remove charges at a proportional ratefrom the pair of charge reservoirs during a second cycle until the firstof the pair of charge reservoirs is depleted of the first charge.

In accordance with one embodiment, a method of forming a neural networkis disclosed. The neural network has n analog multiplier. The analogmultiplier has a pair of charge reservoirs, wherein the pair of chargereservoirs are connected in series. A first charge movement deviceinduces charge movement to or from the pair of charge reservoirs at asame rate. A second charge movement device induces charge movement to orfrom one of the pair of reservoirs, the rate of charge movementprogrammed to one of add or remove charges at a rate proportional to thefirst charge movement device. The first charge movement device, or othermechanism, loads an input charge into a first of the pair of chargereservoirs during a first cycle. The first charge movement device a idthe second charge movement device remove charges at a proportional ratefrom the pair of charge reservoirs during a second cycle until the firstof the pair of charge reservoirs, is depleted of the input charge. Aninput gathering device is used as the mechanism to store charge in thefirst of the pair of reservoirs in conformance with input information.

In accordance with one embodiment, an analog multiplier is disclosed.The analog multiplier has an active pixel comprising a pinned photodiodeand a photodetector, wherein input information to the active pixel isstored on a first input charge reservoir. A second charge reservoir iscoupled to the first reservoir by a transfer gate positioned between thefirst charge reservoir and the second charge reservoir, wherein a firstrate of charge of movement may be controlled by the transfer gate. Asecond charge movement device is coupled to the second charge reservoir,wherein a second rate of charge movement may be programmed in proportionto that of the first rate of charge movement. An input charge is loadedinto the first charge reservoir only during a first cycle and thetransfer gate and the second charge movement device chargeproportionally during a second cycle until the first charge reservoir isdepleted to produce a charge multiplication on the second chargereservoir at the end of the second cycle.

In accordance with one embodiment, a multiplier is disclosed. Themultiplier has a pair of charge reservoirs, wherein each of the pair ofcharge reservoirs are coupled to a gated charge movement device. Thegated charge movement device is programmed so a rate of charge movementis proportional, the gated charge movement device stopping chargemovement once one of the pair of charge reservoirs is depleted.

In accordance with another embodiment, a weighted summer is disclosed.The weighted summer consists of a single charge reservoir. A pluralityof input current movement devices is coupled to the single chargereservoir where for each of the input current movement devices a rate ofcurrent movement conform to weight multiplicands and are proportional toan output charge movement device rate of charge movement. A conductiontime of each output charge movement device during a first cycle conformsto an input value. The charge added or removed during the first cycleinto the Single charge reservoir represents a weighted sum of the inputvalues. During a second cycle the output charge movement devices willone of add or remove charge to return the single charge reservoir to itsoriginal level, a time it takes to return to the original valuerepresenting a sum of input value times weighted by rates of movement ofthe proportional input charge movement devices.

In accordance with one embodiment, a weighted summer is disclosed. Theweighted summer one of adds or removes charge from a plurality of weightcharge movement devices at a rate proportional to an output chargemovement device rate, for a time conforming to input values during afirst cycle. An output charge movement device one of adds or removescharge to change a charge level to an original charge level during asecond cycle. An output time being a weighted sum representation ofinput times weighted by the proportional to output charge movementdevice rates of the weight charge movement devices.

BRIEF DESCRIPTION OF THE DRAWINGS

The present application is further detailed with respect to thefollowing drawings. These figures are not intended to limit the scope ofthe present application but rather illustrate certain attributesthereof. The same reference numbers will be used throughout the drawingsto refer to the same or like parts.

FIG. 1 shows a cross-sectional view of a buried pin diode structureshowing active doping profiles;

FIG. 2A shows a spill and fill circuit;

FIG. 2B shows an energy diagram from a storage well SW charge reservoirinto a floating diffusion FD charge reservoir for the spill and fillcircuit of FIG. 2A;

FIG. 3 shows the spill and fill circuit of FIG. 2A further coupled to areset mechanism (RST) and to a source follower (SF) for reading out thevoltage of the floating diffusion (FD) through a select line (SEL) to abus (COL BUS).

FIG. 4 is a block diagram showing an exemplary embodiment of a neuralnetwork architecture forming a basis of the charge domain mathematicalengine in accordance with one aspect of the present application;

FIG. 5 is block diagram showing air exemplary embodiment of a pinnedphotodiode (PPD) with a two-dimensional shift register in accordancewith one aspect of the present application;

FIG. 6A shows a top level view of a CCD shift register in accordancewith one aspect of the present application;

FIG. 6B shows a cross sectional view of, said CCD shift register alongthe poly finger in accordance with one aspect of the presentapplication;

FIG. 6C shows a cross section view of said CCD shift register cuttingacross the poly fingers in accordance with one aspect of the presentapplication;

FIG. 6D shows different configurations of CCD shift registers where datamay be moving vertically aced then horizontally to alter the flow ofinformation in different directions;

FIGS. 7A-7B shows the concept of systolic rearrangement ofmultiplication and sum coefficients to illustrate the efficiency thatmay be gained using the CCD shift register or other means to provideweights and inputs values to the weighted summers of a neural network inoptimized ways (re-arrange the provision of the coefficients to theweighted summers) in accordance with one aspect of the presentinvention;

FIGS. 8A-8B illustrates the concept of coupled charge reservoirs coupledtogether by first charge movement means and a proportional chargemovement means proportional to the first coupled only to one of thecharge movement means, FIG. 8A shows this configuration using capacitorsas charge reservoirs and current sources as charge movements devices andFIG. 8B shows a similar configuration using a pinned photodiode storagewell, floating diffusions and transfer gates;

FIG. 9 shows a crossbar that might be used to couple pulses or currentsource weights through switch fabric.

FIG. 10 shows a time weighted crossbar that can sum a weighted charge toan output ode and also shift the summing of such a charge over severalframes in time;

FIG. 11 shows a depleted junction transfer gate that could be used toreduce charge injection for switching devices or reduce ringing incurrent sources; and

FIG. 12 is a block diagram showing an exemplary embodiment of a weightedsummer with a pulse output in accordance with one aspect of the presentapplication.

DESCRIPTION OF THE APPLICATION

The description set forth below in connection with the appended drawingsis intended as a description of presently preferred embodiments of thedisclosure and is not intended to represent the only forms in which thepresent disclosure may be constructed and/or utilized. The descriptionsets forth the functions and the sequence of steps for constructing andoperating the disclosure in connection with the illustrated embodiments.It is to be understood, however, that the same or equivalent functionsand sequences may be accomplished by different embodiments that are alsointended to be encompassed within the spirit and scope, of thisdisclosure.

It is desirable to couple the charge stored in reservoirs directly tothe multipliers of the machine learning input layer. Referring to FIG.4, a block diagram showing a neural network architecture 40 forming thebasis of the present application may be seen. In the neural networkarchitecture 40, the circles 42 are neurons or in the case of the inputlayer the input voltage, charge, current, waveform, or digital word. Thelines 44 are multipliers which multiply the input information by aweight (w). The result is fed to a decision circuit and that output inturn is fed to the next layer. As each neuron, containing a summer ofweighted inputs potentially a bias and potentially a decision circuit,may be connected to many neurons m the following layers, therefore thenumber of weights can be very large.

Based on the above, if one could replace the input layer with chargereservoirs such as SW or FD, and utilize this charge within themultipliers connecting this input layer to the first inner layerdirectly, then one could eliminate the latency, power and informationloss due to noise associated with the coupling and digitizationcircuits.

Referring to FIG. 5, once a charge is stored in a reservoir such as SWor PD, it is possible to, store that charge in a charge coupled shiftregister 50 as shown in FIG. 5. The shift register 50 may be formed of aplurality of cells 52. The shift register 50 may move the charge withoutloss of fidelity of the charge information. It is also possible to movethe charge along multiple axis and to combine charges held withinspecific reservoirs. Multiple shift registers 50 can also be used tomove multiplicand information in different directions and at differentspeeds.

In FIG. 5, a pinned photodiode (PPD) may be represented by the largerectangle at the top left. It delivers charge through the TG to a chargereservoir. It is possible to keep loading the charges vertically andthen move them horizontally based upon the construction of the shiftregister 50. In this way it is possible to temporarily store chargeinformation, in a small area, with high fidelity. It is also possible toinduce a charge in one reservoir to flow into a reservoir with anexisting charge to perform summation.

FIG. 6A-6D depict multiple cross-sectional views of a charge coupleddevice (CCD) shift register 60. The CCD shift register 60 allows for Xand Y movement of stored content.

It is common to utilize mathematical constructions to improve theefficiency of multiplies in a machine learning system. For example, inmatrix multiplication it is common to move multiplicands throughdifferent arrangements such that they may be efficiently re-used withouthaving to re-load the information. Systolic structures are an examplewhich may be used to reduce the number of times multiplicands have to beloaded and which make use of prior calculations. It would be desirableto utilize the charge coupled shift register to organize the chargemultiplicands in conformance with these types of mathematical efficiencyimprovements and in some cases to further utilize the charge coupledshift register to combine the charges for summation.

Referring to FIGS. 7A-7B, the concept of a systolic array may bedisclosed. Systolic arrays reduce memory loading and organize data intorecursive or efficient constructs to increase the efficiency of matrixmultiplication. It is useful to implement systolic techniques with CCDshift registers as the operands can easily be moved through the shiftregister at different speeds and in different directions as required bythe different systolic implementations.

FIGS. 8A-8B shows a charge based analog multiplier in multipleimplementations, in FIG. 8A, an implementation 80 where capacitors areused for charge storage is shown where switches S1 and S2 are used toload the input charge reservoir C1 (S1 off, I1 is off, I2 is off, S2 isturned on, current source 82 is tuned on for, a time, switch S2 turnedoff at the end of this cycle) during a first cycle. In FIG. 8B, a pinnedphotodiode PPD is shown charging a reservoir SW the same way as thecurrent source 82 and switch S2 charge the C1 by exposing it to lightfor a time. In both cases the input charge reservoir (C1 in one case andSW in the other) is filled with charge during a first cycle.

In the second cycle S1 in FIG. 8A is closed (S2 being open). The currentsources I1 and I2, which are proportional in magnitude, are turned on.C1 is charged by a current magnitude of I1+I2, and C2 is charged by acurrent magnitude of I2. Node is monitored until the charge on C1 iscompletely dissipated (voltage across it reaches zero). This takesQc1/(I1+I2) time where Qc1 was the charge introduced on C1 during thefirst cycle. C2 is charged by I2 only for this Qc1/(I1+I2) time whichmeans it will see a charge of I2*Qc1/(I1+I2). This means it will receivethe charge C1 multiplied by the ratio of I2/(I1+I2). By controllingI2/(I1+I2) one has set a multiplier gain.

In an analogous way, in FIG. 8B, the charge, on the pinned photodiodePPD may be moved by a field into the floating diffusion FD at a ratecontrolled by the TG path. A second charge path through the TG1 alsofills the FD at a rate proportional to the rate of charge movement fromSW. The time it takes to deplete SW is Qc1/i1=t. A current i1+i2, isflowing into FD for a time t, therefore Qc1*(i1+i2)/i1 is the charge onFD. Thus, one has effectively multiplied the charge by (i1+i2)/i1.Instead of a pinned photodiode a CCD array or other floating diffusioncould be the source of i1. FD may them be read into voltage or currentby a coupling circuit or may be used for further calculation.

By coupling the output of the PPD multiplier to a CCD shift register, atwo dimensional CCD shift register or a second CCD shift register may beused to sum charges as if they were entering a neuron. If a systolicarchitecture is used then the charge reservoirs may be coupled toappropriate operands as they move through the CCD array and the resultsmay be summed into the input reservoir of a multiplier or the resultcould be re-injected into another shift register cell for re-use. Forbroadcast topologies the CCD shift register may be used to createmultiple copies of an input to load an x operand into multiplemultipliers.

It would therefore be useful to store multiplicands in one or more CCDarrays and then move the information through the arrays in conformancewith systolic arrangements so as to minimize memory loading andmultiplier efficiency.

It would be useful to allow the loading of multiple inputs into saidfirst reservoir at the same time. This may be accomplished by summing aknown charge from multiple weighted inputs, such as the outputs ofmultiple neurons from a previous layer, into said first multiplierreservoir. FIG. 9 shows the concept of a crossbar 90. The crossbar 90 isan assembly of individual switches between a set of inputs and a set ofoutputs. The switches may be arranged in a matrix. If the time weightedcrossbar 90 has M inputs and N outputs, then the crossbar has a matrixwith M×N cross-points or places where the connections cross. At eachcross-point is a switch; when closed, it connects one of the inputs toone of the outputs. A given crossbar is a single layer, non-blockingswitch. Non-blocking switch means that other concurrent connections donot prevent connecting other inputs to other outputs. As may be seen inFIG. 9, metal lines 92 come together and switches between them may beturned on to connect lines together on different layers or the samelayers of metal or other conductor. Several crossbars can produce asignificant fanout. A gated current source 94 may be coupled throughsuch an arrangement.

It would be useful to allow the loading of multiple inputs into saidfirst reservoir at the same time. This may be accomplished by summing aknown charge from multiple weighted inputs, such as the weighted outputsof multiple neurons from a previous layer, into said first multiplierreservoir. FIG. 10 shows one possible configuration of a time weightedcrossbar 100, however, for now assume the second row of switches isclosed. In this case connected paths are further coupled to currentsources 102 of the same magnitude. Paths do not start charging until astored voltage, such as an NVM voltage, matches a ramp voltage asdetermined by comparators 104. This produces a charge proportional tothe stored voltage since the currents are proportional and ramp aregenerated from the same source. These currents may be injected into afloating diffusion or optically coupled into a diffusion or useddirectly if capacitors or other storage elements are used for themultiplier. This time delay crossbar 100 may be addressed using relativeor direct addressing and allows flexible neural network configurationseven though the neurons have a specific physical location. The result isthat the weights are set by current magnitudes and input values by time.For subsequent layers, or layers with charge inputs such as PPD inputs,the output of each weighted summer can be time and therefore thecomparators 104 are not necessary—the output of previous neurons can beapplied directly to gate the switches.

Current magnitudes may come from a dynamic or from an NVM memory. Thismay be an analog memory such as a ferroelectric memristor. It could bean analog floating gate or flash memory. Or it could be a DNA memory.DNA memory has recently shown great promise in producing analog ordigital memory in a very small area like 3 nm with a very long lifetime.Ferroelectric memristors such as those developed by Panasonic have beenshown capable of producing accurate analog values.

Neuromorphic spiking networks are energy efficient because they onlyturn on neural, pathways when the controlling neuron weighted inputsummer reaches a threshold, leaving neurons which do not accumulatesufficient input charge unused. It would be useful to modify theweighted summer described in this application to allow such animplementation when said weighted summer is used to create a neuron.This can be done by coupling a comparator to the first/input chargereservoir and once the charge on this reservoir reaches a level aninterrupt is generated forcing the controller to couple the output ofthe neuron to its appropriate connection within the desired neuralnetwork. Some neuromorphic spiking networks also have the retirement formagnitude and/or time delay information. Time delay may be introducedthrough repeating the ramp in the time delay crossbar multiple times andthrough the use of a second set of switches 106 in FIG. 10. For exampleif the ramp were repeated five times and a controller provided a fivebit word indicating on which ramp the current should be applied then asimple counter could be used to determine when to turn on said secondswitch to implement said time delay by only allowing current to flow ifit matches the appropriate five (5) bit delay word.

In certain cases it may be more efficient to separate the chargereservoirs completely rather than coupling them in series. In this easethe first charge reservoir charges during, a first cycle and during asecond cycle is discharged by a charge movement means at a controlledrate until it is depleted. During this same second cycle a second chargemovement means, programmed to be of proportional magnitude to thatcharging the first, charges the second charge reservoir until the chargeon the first charge reservoir is depleted. Now the charge on the secondcharge reservoir will be that of the first multiplied by the ratio ofthe rates of charge movement. For example if the charge movement meanswere current sources, and I1 were depleting the first charge reservoirand I2 charging the second, then the charge on said second chargereservoir at the end of the seed cycle would be I2/I1*Q1 where Q1 is theinitial charge on the first charge reservoir. The charge movement meanscould be a MOSFET transfer gate, a graded junctions or other devicescapable of controlling charge while also being started or stopped.

To reduce charge injection and allow use of extremely small equivalentcapacitances, the transfer gates are created with depleted junctionMOSFETs whose construction is also designed to minimize overlapcapacitance. An example is shown in FIG. 11.

Referring to FIG. 12 an embodiment showing weighted summer 120 may beconsidered. Here a single charge reservoir is shown consisting of thegate of MN1 which is also connected to C1 (which could be a capacitor orfloating diffusion), the drain of the gating MOSFETs 122 and currentsource 126 also known as Iout. Charge movement device 124 labelled w1and wn and bias b1 are programmed in conformance with desired weightinputs and in proportion to current source Iout 126. These weight inputsare gated by time inputs a1, an, and b which are shown connected to abuffer driving the gates of MOSFETs 122. During a reset the gate of MN1is pulled below its Vt comparator threshold, which will cause the drainof MOSFET M1 to invert and allow inverter 128 to turn on current source126 until the MN1 gate reaches its switching threshold after which it isswitched off. In a first cycle, the time plurality of pulse inputs a1 .. . an and b effectively allow the weights to flow for a given amount oftime resulting in a weighted charge to be removed from the chargereservoir at the gate of MN1. Once this current is removed MN1's drainwill again flip its state and cause the inverter 128 to turn on thecurrent source Iout which will replace the charge removed by theweighted inputs. The time it takes to do so will represent a weightedsum output pulse at aout.

While embodiments of the disclosure have been described in terms ofvarious specific embodiments, those skilled in the art will recognizethat the embodiments of the disclosure may be practiced withmodifications within the spirit and scope of the claims

What is claimed is:
 1. A weighted summer comprising: a single chargereservoir; a plurality of input charge movement devices each coupled tothe single charge reservoir, each one of coupling or removing charges toor from the single charge reservoir in a first cycle, wherein for eachof the input charge movement devices a rate of charge movement conformsto weighted multiplicands and are proportional to an output chargemovement device rate of charge movement; and an output charge movementdevice one of coupling or removing the charges to or from the singlecharge reservoir so as to return the single charge reservoir to astarting charge level during a second cycle after which charge movementends.
 2. The weighted summer of claim 1 wherein: the plurality of inputcharge movement devices couple or remove the charges at ratesproportional to the rate that the output charge movement device willcouple or remove the charges during the second cycle, but where theplurality of input charge movement devices are each individually gatedin time in conformance with input information and; wherein during thesecond cycle a time during which the output charge movement device iscoupling or removing the charges to return the single charge reservoirto the starting charge level represents an output of the weightedsummer.
 3. The weighted summer of claim 1, wherein the summer comprisesa spiking circuit having a comparator, the comparator initiating aninterrupt to a controller circuit when the single charge reservoirreaches a predetermined level.